Thermionic frequency changing or modulating device



Feb. 12, 1929. 1,702,001

E. w. a. GILL ET AL THERMIONIC FREQUENCY CHANGING OR MODULATING' DEVICE Filed Feb. 24, 1928 INVENTOR ERNEST W.B. GXLL BY R ERT H- DNALDSON AT'Q NEY Patentecl' Feb. 12, 1929.

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EBNEST WALTER BBJUDENELL GILL AND ROBERT BONALDSON, F OXFORD,

ENGLAND; SAID GILL ASSIGNQIB, TO RADIO UQRPURALLIOIT'OF AMERICA, A COB- PORA'IION OF DELAWARE.

THERMIONIC FREQUENCY CHANGING: 0R MODULATING DEVICE.

I Application filed- February 534, 1928, Serial No. 25656 1, and in Great Britain February 18, 1927.

An application has. been filed in England, Feb. 18, 1927, which embraces the invention herein described. t

This invention relates to thermionic "fre- 5 quency changing or modulating devices, and is particularly suitable for use in wireless telegraphy and telephony.

In the {specification of British Patent No. 252,079, l ay18, 1926-, was described a valve such that when its anode is maintained at a positive potential with respect to the oath ode while a potential slightly positive or slightly negative with respect to the cathode is appliedtothe outergrid the inner grid being maintainedas a positive potential a critical point can be found at which an increase in inner grid-potentialproduces a decrease ininner grid current and conversely, a decrease in inner grid voltage would cause an increase in innergrid current. This characteristichas, by the inventor and by the prior art been termed. as a negativeresistance characteristic. v

It has alsobeen found, as pointed out hereinafter, and in the above referred to specification that under suitable conditions, the amplification capable of being obtained with valvesso constructed isextremely high. The present invention utilizes such a negative resistance, four-electrode valve in such a inanner" as to derive therefrom, the bone fitsof the higharnplificationoi the valve and also of its negativeresistancecharacteristics which inherently adapt it to, generation of oscillations" According to the present invention a thermionic frequency changing ormodulating device comprises a negative resistance fourclectrode :valvc as described above, means for applyingto-theinput circuit of the said valve a modulating frequency or, frequency to he changed, and'which itseltmay be modulated by signals, and means for maintaining the output circuit of said valve inoscillation at a frequency substantially different from the first mentioned frequency whereby the a1nplitudeof the oscillations is controlled in accordance with the saidfirst mentioned frequency The invention is illustrated in the drawings accompanying the provisional specification, in which, i I

Figure 1. is a circuit diagram and Figure 2 a graphic representation of results obtainable with the invention.

If the incoming oscillation is of shorter wave length-than. the local oscillation, the variation in amplitude of the local oscillations is of the same order asthe incoming oscillations. If the incoming oscillation is of longer wave length, then the variations of amplitude in the local oscillator are in general much larger than.- in the incoming wave. 7

The localoscillation should diii'er widely in wave length from the incoming oscillations or else forced vihrationshniay occur. The :local oscillations are maintained, by negative resistance effects on thcinncl grid of the tour-electrode valve. as pointed out above and in the British, specification referred to, the degree of. negative resistance being'controlled by, the potential applied to the outer grid for aparticular value. offilament. emission;

It the incoming wave is much longer than the local wave, there will be manyKosciHations of the local Wave for, a half Wave of the incoming oscillations, and hence the said local waves will be enormously magnified for one half wave and enormously reduced forthe next half wave. It, on the other hand, the incoming wave is shorter than the local there is only "onexoscillation of'the local wave for several incoming oscillations. The amplitude of the local wave takes up in eilect a mean value dependent on ,thecurvature of the inner grid oscillation, potential-outer grid potential curve, as shown in Figure 2. in practice the voltage variation in the latter case of the local waves is generally of the same order as the voltage variationof the incoming waves.

Referring to Figure 1, which shows in circuit diagram form one wayzof carrying out the invention, 1 is the receiving aerial to which is coupled, preferably variably, an oscillatory circuit 2, connected between the outer grid 10 andthccathode 13, of avfour electrode valve 8, of the kind more fully described above and in the prior British Patent" No. 252,079, May 18, 1926. The plate 14: of the valve is connected through a reaction coil, varia-hly coupled to the oscillatory clrcuit 2, a

' battery 4 and a potentiometer to the oathmetres. the input side of a known amplifier, which is 0 in relation thereto.

l 1 very large' change in the amplitude of the osode 13. The inner grid 11 of the valve 3 is connected through an oscillatory circuit 6 and a battery 15 to the cathode. The reaction coil, aerial and oscillatory circuit .2 are tuned to the frequency to be received. e. a frequency corresponding to a wavelength of 60 metres, while the oscillatory circuit 6 is tuned to the lower frequenc e. g. a frequency corresponding toa wave length of 15000 The circuit 6 is'variably coupled to permanently tuned to the lower frequency and comprises two valves 7, 8 the output from the same amplifierbeing rectified by means of a valve 9. The four-electrode valve and the batte'ries associated therewith are so adjusted that the outer gridlO is at approximately the samepotential as the cathode 13,

the inner grid 11 and the'pIate 14: being main-H tained at a-positive potential, say, 20volts as is set forth above and in the said'prior 'Britis h Patent No. 252,079, May 18, 1926, for

a particular cathode emission the'inner grid shows a negat ve resistance and the oscillatory circuit 6'will therefore be maintained inroscillation'at its own wave length. The

7 degree of negative resistance is critically de pendent upon the outer grid potential, a yery small change in this potential resulting in a cillations in the circuit 6. The negative resistance effects can only be obtained over a small range of outer grid potenti'ahthe rela tion between the outer grid potential and amplitude of oscillation within this, range following. a curve generally as shown in Figure'2'. A potentiometer may be employedjto :adjust the outer grid 'to operate at-either of the points A or B of the curve shown in Figure 2. I

" i "The, negative resistance effect is also de- I adjusted by the potentiometer 5, which is 8111- ployed to adjust-the valve so that it is working at'therequired pendent on the magnitude of the platepoten- 'tial for a given potential on the outer grid,

and the plate potential may conveniently be point corresponding to A. 'orB of the curve." W r p In a modification'the reaction coil in the.

plate circuit of the four-electrode valve is dispeused'with. the said plate being connected to the same battery as'isthe inner grid.

In a further modification, suitable for re ceiving unmodulated continuous waves, an

independent heterodyne is provided or alternatively the four-electrode valvema'y be I "caused to maintainthe highifrequency circuit in oscillation by ineansof a-reaction coil included in its anode circuit;

7 It will be seen that the present: invention [possesses the two principal advantagesf-of i supersonic hetero'dyne receivers, namely, that amplificationmay be effected at: aloweiifre-l Under these conditions,

quency than that of the received signals, and one which does not require to be altered with thereof we do not wish tolimit ourselves thereby except as marked outin the following claims v 1 I. A thermionic modulating device comprising a four electrode valve so'constructed and arranged that under predetermined opcrating conditions increase in inner grid potential causes adecrease in inner grid current, an oscillatory input circuit connected between the outer grid and cathodeof said valve, an oscillatory output circuit tuned to the required frequency of oscillation of said valve and effectively connected between thev inner grid thereof and the catho-de,'meansfor applying potential to the anode ofsaid valve and to the inner grid thereof, and means for applying to the input circuit ofsaid valve a modulating frequency whereby theamp'litude of the oscillations insaid outp'utcircuit is controlled in accordance with the oscillations in said first named oscillation circuit.

. 21A thermionic modulating. device --,com-

prising a four electrode valveso constructed...

and arranged thatu'nder predetermined operating conditions an increase in inner grid potential causes'a decrease'in" inner grid current, an oscillatory input circuit connected- .betweenthe-outer grid and cathodeof said valve,a circuit connected between the anode and cathode of said valve, meansfor'coupling said last named'circuit to said oscillatory c1rcuit comprising an inductance coil in said last namedcircuit, an oscillatory output cir-l cuit tuned to the required frequency of oscil lation; of said valve connected; between the inner grid thereof-and the cathode, meansfor applyingrpotentialto the anode of saidgvalv'e and tothe inner grid thereof, and means for modulating frequency, whereby the amplitude of the'oscilla'tions insaid output circuit is controlled in accordance'with the oscillations in said input circuit. 0

3. A thermionic modulatin prising a four electrode valve aving anode,

cathode and two grid electrodes, said 'elec-i .tro'des'being so arranged that when a critical potential is applied to the outer grid anin crease in inner-grid potential will cause a de-'" device com-' applying to the input circuit o fysaid valve acrease in inner gridacurrentjan'inputoscil latory circuit including an inductance a variable capacity connected between the outer grid and the cathode of said valve, a reaction circuit including a source of potential, connected between the anode and the cathode of said valve, an inductance in said reactance circuit coupled to the inductance in said input circuit, an oscillatory output circuit con nected between the inner grid and the cathode of said valve, means for maintaining oscillations a predetermined frequency therein including a capacity and an inductance and a source of potential, and means for varying the amplitude of the oscillations in said last named oscillation circuit including means for applying to the input oscillatory circuit oscillations at a diflierent frequency.

4. The method of signalling by means of a four electrode valve having cathode, anode and inner and outer grid electrodes and oscillation circuits connected between said inner and outer grids and said cathode which consists in, setting up oscillations at signal frequency in the circuit connected between said outer grid and said cathode, setting up oscillations at a different frequency in said circuit coupled between said inner grid and said cathode, applying potential to said inner grid and said anode, and causing said first named oscillations to vary the amplitude of said last named oscillations in accordance with said first named oscillations.

ERNEST WALTER BRUDENELL GlLL. ROBERT HOPE DONALDSON. 

